Silver halide emulsions sensitized with cyanine dyes containing a pyrrolo(2,3-b) quinoxaline or pyrrolo(2,3-b)pyrazine nucleus

ABSTRACT

NOVEL CYANINE DYES ARE PROVIDED WHICH FEATURE A PYRROLO(2,3-B) QUINOXALINE NUCLEUS OR A PYRROLO(2,3-B)PYRAZINE NUCLEUS, JOINED AT THE 3-CARBON ATOM THEREOF TO THE METHINE LINKAGE OF THE CYANINE DYE. PHOTOGRAPHIC SILVER HALIDE EMULSIONS CONTAINING THESE DYES ARE ALSO PROVIDED.

United States Patent SILVER HALIDE EMULSIONS SENSITIZED WITH CYANINEDYES CONTAINING A PYRROL0[2,3-b] QUINOXALINE 0R PYRROL0[2,3-b]PYRAZlNENUCLEUS John D. Mee, Donald W. Heseltine, and Wilbur S. Gaugh,

Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y.

No Drawing. Filed Feb. 15, 1968, Ser. No. 705,595 Int. Cl. G03c 1/08,1/10, 1/28 US. Cl. 96-420 30 Claims ABSTRACT OF THE DISCLOSURE Novelcyanine dyes are provided which feature a pyrrolo[2,3-b]quinoxalinenucleus or a pyrrolo[ 2,3-b]pyrazine nucleus, joined at the 3-carbonatom thereof to the methine linkage of the cyanine dye. Photographicsilver halide emulsions containing these dyes are also provided.

This invention relates to novel cyanine dyes and novel photographicemulsions containing such dyes. The novel dyes of this invention areespecially useful as electron acceptors and spectral sensitizers fordirect positive photographic silver halide emulsions.

It is known that direct positive images can be obtained with certaintypes of photographic silver halide emulsions. For example, photographicemulsions have been proposed for this purpose comprising an electronacceptor and silver halide grains that have been fogged with acombination of a reducing agent and a compound of a metal moreelectropositive than silver. One of the advantages of such directpositive emulsions is that the high-light areas of the images obtainedwith these materials are substantially free from fog. However, knownmaterials of this type have not exhibited the high speed required formany applications of photography. Also, such known materials have notshown the desired selective sensitivity, especially to radiation in thegreen to red region of the spectrum. It is evident, therefore, thatthere is need in the art for improved direct positive photographicmaterials having both good speed and desirable sensitivity to longerWavelength radiations.

It is, accordingly, an object of this invention to provide a new classof cyanine dyes. Another object of this invention is to provide novelcyanine dyes which function as effective electron acceptors and spectralsensitizers in photographic silver halide emulsions. A further object ofthis invention is to provide novel photographic silver halide emulsions,including direct positive photographic emulsions, containing one or moreof the novel dyes of the invention. Another object of this invention isto provide photographic emulsions containing novel cyanine dyes and aphotographic color former. Still another object of this invention is toprovide photographic elements comprising a support having thereon atleast one layer of the novel emulsions of the invention. Other objectsof this invention will be apparent from this disclosure and the appendedclaims.

We have now found that certain cyanine dyes derived from l-substitutedpyrrolo[2,3-b]pyrazines and 1-substituted pyrrolo[2,3-b]quinoxalines areoutstanding electron acceptors and spectral sensitizers for directpositive type of photographic silver halide emulsions. They providesuperior reversal systems, especially with fogged silver halideemulsions, that are characterized by both good speed and desiredselective sensitivity to radiation in the green to red region of thespectrum with maximum sensitivity occurring in most cases in the regionof about 500'- 600 nm. The images produced with these new directpositive emulsions are clear and sharp and of excellent contrast.

The novel cyanine dyes of the invention comprise first and second 5- to6-membered nitrogen containing heterocyclic nuclei joined together by amethine linkage containing from 2 to 3 carbon atoms in the methine chain(including those linkages wherein a methine group is substituted byalkyl, aryl or heterocyclic substituents); the first of said nucleibeing selected from a pyrrolo[2,3-b] quinoxaline nucleus or apyrrolo[2,3-b]pyrazine nucleus joined in each case at the 3-carbon atomthereof to said linkage; and, said second nucleus being selected from(a) a heterocyclic nitrogen containing nucleus of the type used in theproduction of cyanine dyes, when said linkage is a dimethine linkage,and (b) when said linkage is a trimethine linkage, said second nucleusis selected from the group consisting of a Z-arylindole nucleus, apyrrolo- [2,3-b1quinoxaline nucleus and a pyrrolo[2,3-b]pyrazinenucleus, each of said nuclei being joined at the 3-carbon atom thereofto said trimethine linkage. Preferably, the second nucleus is adesensitizing nucleus.

The preferred class of novel cyanine dyes of the invention include thoserepresented by the following general formula:

C(2-pyridyl)=; C(2-thienyl)=; etc.; R represents an alkyl group,including substituted alkyl (preferably a lower alkyl containing from 1to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl,hexyl, cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups,(preferably a substituted lower alkyl containing from 1 to 4 carbonatoms), such as a hydroxyalkyl groups, e.g., fl-hydroxyethyl,w-hydroxybutyl, etc., an alkoxyalkyl group, e.g., S-methoxyethyl,w-butoxybutyl, etc., a carboxyalkyl group, e.g., ,H-carboxyethyl,w-carboxybutyl, etc., a sulfoal'kyl group, e.g., fi-sulfoethyl,w-sulfobutyl, etc., a sulfatoalkyl group, e.g., fi-sulfatoethyl,w-sulfatobutyl, etc., an acyloxyalkyl group, e.g., fi-acetoxyethyl,'y-acetoxypropyl, w-butyryloxybutyl, etc., an alkoxycarbonylalkyl group,e.g., fi-methoxycarbonylethyl, w-ethoxycarbonylbutyl, etc., or anaralkyl group, e.g., benzyl,

' phenethyl, etc.; an alkenyl group, e.g., allyl, l-propenyl,

2-butenyl, etc.; or, an aryl group, e.g., phenyl, tolyl, naphthyl,methoxyphenyl, chlorophenyl, etc.; R represents an alkyl group, e.g.,methyl, ethyl, propyl, isopropyl, butyl, decyl, dodecyl, etc., or anaryl group, e.g., phenyl, tolyl, naphthyl, etc.; R and R each representsa hydrogen atom, an alkyl group (preferably a lower alkyl containingfrom 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl,butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., or an aryl group, e.g.,phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl, methoxyphenyl, etc.;and, R and R taken together can represent the non-metallic atomsnecessary to complete a pyrrolo[2,3-b]quinoxaline nucleus; R representsa hydrogen atom or an aryl group, e.g., phenyl, tolyl, naphthyl,chlorophenyl, nitrophenyl, methoxyphenyl, etc.; X represents an acidanion, e.g., chloride, bromide, iodide, thiocyanate, sulfamate,perchlorate, p-toluenesulfonate, methyl sulfate, ethyl sulfate, etc.;and Z represents the non-metallic atoms necessary to complete aheterocyclic nucleus of the type used in cyanine dyes, and preferably adesensitizing nucleus, containing from 5 to 6 atoms in the heterocyclicring, which nucleus may contain a second hetero atom such as oxygen,sulfur, selenium or nitrogen, such as the following nuclei:

a thiazole nucleus, e.g., thiazole, 4-rnethylthiazole, 4-phenylthiazole, S-methylthiazole, S-phenylthiazole, 4,5-dimethylthiazole, 4,5-diphenylthiazole, 4 (2 thienyl) thiazole,benzothiazole, 4-chlorobenzothiazole, 4- or S-nitrobenzothiazole,S-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole,4-methylbenzothiazole, S-methylbenzothiazole, 6-methylbenzothiazole,6-nitrobenzothiazole, S-bromobenzothiazole, 6-bromobenzothiazole,S-chloro-6-nitrobenzothiazole, 4-phenylbenzothiazole,4-methoxybenzothiazole, S-methoxybenzothiazole, 6-methoxybe'nzothiazole,S-iodobenzothiazole, 6-iodobenzothiazole, 4-ethoxybenzothiazole,ethoxybenzothiazole, tetrahydrobenzothiazole,5,6-dimethoxybenzothiazole, 5,6-dioxymethylenebenzothiazole,S-hydroxybenzothiazole, 6-hydroxybenzothiazole, naphtho[2,1-d]thiazole,naphtho[1,2-d]thiazole, naphtho 2,3-d] thiazole, S-methoxynaphtho[2,3-d] thiazole, S-ethoxynaphtho[ 1,2-d] thiazole, S-methoxynaphltho-[2,1-d]thiazole, 7-methoxynaphtho[2,1-d]thiazole, 4'-methoxythianaphtheno-7,6-4,S-thiazole, nitro group substitutednaphthothiazoles, etc.;

an oxazole nucleus, e.g., 4-methyloxazole, 4-nitro-oxazole,S-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole, 4-ethyloxazole,4,5-dimethoxazole, S-phenyloxazole, benzoxazole, S-chlorobenzoxazole,S-methylbenzoxazole, S-phenylbenzoxazole, 5- or 6-nitr0benzoxazole,5-chloro-6-nitrobenzoxazole, 6-methylbenzoxazole, 5,6-dirnethylbenzoxazole, 4,6-dimethylbenzoxazole, 5-methoxybenzoxazole,S-ethoxybenzoxazole, 5-chlorobenzoxazole, 6-methoxybenzoxazole,S-hydroxybenzoxazole, 6-hydroxybenzoxazole, naphth [2,1-d] oxazole,naphth- [1,2-d]oxazo1e, nitro group substituted naphthoxazoles, etc.;

a selenazole nucleus, e.g., 4-rnethylselenazole, 4- nitro selenazole,4-phenylselenazole, benzoselenazole, S-chlorobenzoselenazole,S-methoxybenzoselenazole, 5-hydroxybenzoselenazole, 5- or6-nitrobenzoselenazole, 5- chloro 6 nitrobenzoselenazole,tetrahydrobenzoselenazole, naphtho [2,1-d] selenazole, naphtho 1,2-d]selenazole, nitro group substituted naphthoselenazoles, etc.,

a thiazoline nucleus, e.g., thiazoline, 4-methylthiazoline,

4-nitr0thiazoline, etc.;

a pyridine nucleus, e.g., 2-pyridine, 5-methyl-2-pyridine, 4-pyridine,3-methyl-4-pyridine, nitro group substituted pyridines, etc.;

a quinoline nucleus, e.g., 2-quinoline, 3-methyl-2-quinoline,5-ethyl-2-quinoline, 6-chloro-2-quinoline, 6-nitro- Z-quinoline,8-chloro-2-quinoline, 6-methoxy-2-quinoline, S-ethoxy-Z-quinoline,8-hydroxy 2 quinoline, 4- quinoline, 6 methoxy-4-quinoline,6-nitro-4-quinoline, 7-rnethyl-4-quinoline, 8-chloro-4-quinoline,1-isoquinoline, 6-nitro-1-isoquinoline, 3,4-dihydro-l-isoquinoline,3-isoquinoline, etc.;

a 3,3-dialkylindolenine nucleus, preferably having a nitro or cyanosubstituent, e.g., 3,3-dimethyl-5 or 6-nitroindolenine, 3,3-dimethy1-5-or 6-cyanoindolenine, etc; and

an imidazole nucleus e.g., imidazole, l-alkylimidazole,

1-alkyl-4-phenylimidazole, 1-alkyl-4,S-dimethylimidaZ- ole,benzimidazole, l-allrylbenzirnidazole, 1-aryl-'5,6-dichlorobenzimidazole, 1-alkyl-lH-naphthimidazole, 1- aryl-3H-naphth1,2-d] imidazole, l-alkyl-S-methoxy- 1H-naphth[ 1,2-d]imidazole, or

an imidazo[4,5 b]quinoxaline nucleus, e.g., 1,3dialkylimidazo[4,5-b]quinoxaline such as 1,3-diethy1imidazo-[4,5-b1quinoxaline, 6-chloro-1,3-diethylirnidaz0 [4,5-b] quinoxaline,etc., 1,3-dialkylenylimidazo[4,5-b]quinoxaline such as1,3-diallylimidazo[4,5-b1quinoxaline, 6- chloro-1,3-diallylimidazo[4,5-b]quinoxaline, etc., 1,3- diarylimidazo[4,5-b]quinoxaline such as1,3-diphenylimidazo[4,5-b]quinoxaline, 6-chloro 1,3 diphenylimidazo[4,5-b] quinoxaline, etc.;

a 1,3,3-trialkyl-3H-pyrrolo[2,3-b]pyridine nucleus, e.g.,

1,3 ,3-trimethyl-3H-pyrrol0 [2,3-b] pyridine, '1,3,3-triethyl-3H-pyrrolo [2,3-b] pyridine, etc.;

a thiaZ0lo[4,5-b]quinoline nucleus; and the like.

Nuclei wherein Z represents an irnidaz0[4,5-b]quinoxaline nucleus, a1,3,3-trialkyl-3H-pyrrolo[2,3-b] pyridine nucleus, athiazolo[4,5b]quinoline nucleus, at nitro group substituted thiazole,oxazole, selenazole, thiazoline, pyridine, quinoline,1,3,3-trialkylindolenine, or imidazole nucleus are desensitizing nuclei.

The dyes defined above are powerful electron acceptors and spectralsensitizers for direct positive photographic silver halide emulsions. Inaddition, they are also useful desensitizers in emulsions used in theprocess described in Stewart and Reeves, US. Pat. No. 3,250,618, issuedMay 10, 1966.

As used herein desensitizing nucleus refers to those nuclei which, whenconverted to a symmetrical carbocyanine dye and added to gelatin silverchlorobromide emulsion containing 40 mole percent chloride and 60 molepercent bromide, at a concentration of from 0:01 to 0.2 gram dye permole of silver, cause by electron trapping at least an percent loss inthe blue speed of the emulsion when sensitomerically exposed anddeveloped three minutes in Kodak developer D-l9 at room temperature.Advantageously, the desensitizing nuclei are those which, when convertedto a symmetrical carbocyanine dye and tested as just described,essentially complete desensitize the test emulsion to blue radiation(i.e., cause more than about to loss of speed to blue radiation).

Another highly useful class of novel cyanine dyes of the inventioninclude those represented by the following wherein R R R R R and X areas previously de fined, R represents an alkyl group (preferably a loweralkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl,isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., or an arylgroup, e.g., phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl,methoxyphenyl, etc., or a heterocyclic radical containing from 5 to 6atoms in the heterocyclic ring and having a hetero nitrogen, oxygen orsulfur atom, preferably a heterocyclic radical selected from pyridyl(e.g., 2-, 3- or 4-pyridyl), 3-indolyl, or 2 thienyl; R represents ahydrogen atom or an aryl group, e.g., phenyl, tolyl, naphthyl,chlorophenyl, nitrophenyl, methoxyphenyl, etc.; and, D represents thenon-metallic atoms necessary to complete a 2-arylindole nucleus (e.g., al-al kyl (or aryl)-2-phenylindole, a 1- alkyl (oraryl)-5-nitro-2-phenylindole, etc.) a pyrrolo [2,3-b]quinoxaline nucleus(e.g., 1-butyl-7-chloropyrrolo- [2,3-b] quinoxaline,1-methyl-2-p-tolylpyrrolo 2,3-b] quinoxaline, etc.) or apyrrolo[2,3b]pyrazine nucleus (e.g., 1-methylpyrrolo[2,3-b1pyrazine,etc.)

b Typical representative dyes of this invention are listed elow:

1 ,3 '-diethyl-6'-nitro-3-pyrrolo 2,3-b quinoxalinothiacarbocyaninep-toluenesulfonate 1 ,3-diallyl-1'-ethylimidazo[4,5-b] quinoXalino-3-pyrrolo [2,3-b quinoxalinocarbocyanine p-toluenesulfonate 1'-ethyll 3,3 -trimethyl-3H-pyrrolo [2,3-b pyrido-3 '-pyrrolo [2,3-bquinoxalinocarbocyanine iodide 6-chloro- 1 '-ethyl- 1 ,3-diphenylimidazo[4,5 -b quinoxalino- 3-pyrrolo [2,3-b] quinoxalinocarbocyaninep-toluenesulfonate 1-ethyl-1,3 ,3-trimethyl--nitroindo-3 -pyrrolo[2,3-b]

quinoxalinocarbocyanine p-toluenesulfonate 1-butyl-7- chloro-3-ethyl-6-nitro-3 -pyrrolo [2,3 -b] quinoxalinothiacarbocyaninep-toluenesulfonate 1,3 -diallyl-1-butyl-7-chloroimidazo [4,5 -b]quinoxalino- 3-pyrrolo[2,3-b] quinoxalinocarbocyanine bromide 1'-butyl-7'-chloro-1,3 3 -trimethyl-5-nitroindo-3 '-pyrrolo [2,3-b]quinoxalinocarbocyanine bromide 3'-ethyl-1-methyl-6'-nitro-2-p-tolyl-3-pyrr0lo[2,3-b]

quinoxalinothiacarbocyanine p-toluenesulfonate1,3-diallyl-1'-methyl-2'-p-tolylimidazo [4,5-b] quinoxalino- 3 -pyrrolo[2,3-b] quinoxalinocarbocyanine p-toluenesulfonate6-chloro-1'-methyl-1,3-diphenyl-2'-p-tolylimidazo- [4,5 -b]quinoxalino-3-pyrrolo [2,3-b] quinoxalinocarbocyanine p-toluenesulfonate1,1, 3 3-tetramethyl-5-nitro -2-p-tolylindo-3 -pyrrolo- [2, 3-b]quinoxalinocarbocyanine p-toluenesulfonate l,1',3,3-tetramethyl-2'-p-tolylpyrrolo [2,3-b pyrido-3pyrrolo[2,3-b]quinoxalinocarbocyanine perchlorate1'-ethyl-1,3,3,S-tetramethyl-S-nitroindo-3'-pyrrolo- [2, 3-b]quinoxalinocarbocyanine p-toluenesulfonate 1,1'-diethyl-11-phenyl-3-pyrrolo [2,3-b] quinoxalino-4- carbocyanine bromide 7'-chloro-3 -ethyl-6-nitro-1-phenyl-8- (2-thienyl) oxa- 3'-pyrrolo [2,3-bquinoxalinocarbocyanine bromide3'-ethyl-1-methyl-6'-nitro-2-p-tolyl-3-pyrrolo[2,3-b]

quinoxalinoselenacarbocyanine bromide1,3'-diethyl-5'-nitro-3-pyrrolo[2,3-b] quinoxalinothiazolinocarbocyaninep-toluenesulfonate 3-ethyl-1'-propyl-3 -pyrrolo [2,3-bquinoxalino-Z-thiaz- 010 [4,5-b] quinolinocarbocyanine bromide5,6-diethyl-3 8'-dimethyl-5-nitro-1-phenyl-3 -pyrrolo- [2,3-b]pyrazinoselenacarbocyanine bromide 1,3-diallyl-1,1-butyl-2-phenylimidazo[4,5-b] quinolino- 3'-pyrrolo [2,3-b] pyrazinocarbocyanine iodide 3'-ethyl-5,6-dimethyl-5-nitro-1-phenyl-3 -pyrrolo- [2,3-bpyrazinothiazolinocarbocyanine iodide 3-ethyl-9-methyl-1,5,6-triphenyl-3-pyrrolo[ 2,3-b] pyrazino-2'-thiazolo [4,5 -b] quinolinocarbocyanineiodide 1,1'-dimethyl-2-(Z-naphthyl) -2'-phenyl-8- Z-thienyl) 3-indolo-3'-pyrrolo [2,3 -b] quinoxalinocarbocyanine bromide 5 ,6-dimethy1-1,1'-diphenyl-8- 3-pyridyl) -3-pyrrolo- [2,3-b] pyrazino-3'-pyrrolo[2,3-b] quinoxalinocarbocyanine bromide 8- 2-furyl) -1-methyl- 1,2-diphenyl-3,3'-pyrrolo [2,3-b]

quinoxalinocarbocyanine perchlorate8-ethyl-1'-methyl-5,6-diphenyl-3-pyrrolo [2,3-b1pyrazino-3 -pyrrolo[2,3-b] quinoxalinocarb ocyanine bromide 2-ethyl-1,1'-dimethy1-8-(Z-naphthyl) -3,3'-pyrrolo- [2,3 -b] pyrazinocarbocyanine bromide1,1'-dimethyl-2, 8-diphenyl-2'-p-tolyl-3 -indolo-3 -pyrrolo- [2,3-b]quinoxalinocarbocyanine perchlorate3'-ethyl-6'-nitro-1-phenyl-3-pyrrolo[2,3-b] pyrazino thiacarbocyaninep-toluenesulfonate 3 -methyl-5-nitro-1'-phenyloxa-3 -pyrr 010 [2,3 -b]pyrazinocarbocyanine p-toluenesulfonate 1,3-dimethyl-1'-phenylimidazo[4,5-b] quinolino-3-pyrrolo 2,3-b pyrazinocarbocyaninep-toluenesulfonate 6-chloro-1,1,3-triphenylimidazo[4,5-b]quinoxalino-3'-pyrrolo [2,3-b] pyrazinocarbocyanine bromide 1',3 ',3'-trirnethy1-1-phenyl-3 -pyrrolo [2,3 -b] pyrazino- 3H-pyrrolo [2,3 -b]pyridocarbocyanine p-toluenesulfonate 1,3,3-trimethyl-5-nitro-1-phenylindo-3 '-pyrrolo [2, 3 -b]pyrazinocarbocyanine p-toluenesulfonate These dyes also function aspowerful electron acceptors and spectral sensitizers for direct positivephotographic silver halide emulsions, as well as being usefuldesensitizers in emulsions used in the aforementioned process describedin Steward and Reeves U.S. Pat. No. 3,250,618, issued May 10, 1966.

The cyanine dyes defined by Formula I above are conveniently prepared,for example, by heating a mixture of (1) a heterocyclic compound of theformula:

wherein n, R X and Z are as previously defined, and R represents methyl,ethyl, benzyl, etc., and (2) a heterocyclic compound of the formula:

(IV) R3 4 Rz-N C-CHO (V) Rl- N\ CH3 [at N/ I 2 or a compound of theformula:

wherein R R R R and X are as previously defined, with (2) a complex ofphosphoryl chloride, phosgene, oxalyl chloride, etc. and dimethylformamide in excess dimethylformamide, as solvent, in approximateproportions of 1 mole of 1) to 3 or more moles of (2). The reactionmixtures are cooled, diluted with ice-water mixture, and then madealkaline by addition of aqueous alkali metal hydroxide solution such asaqueous sodium hydroxide. The product is then separated by conventionalmethods, for example, by extraction of the mixture with awater-insoluble solvent such as chloroform, the residue being purified,if desired, by one or more recrystallizations from appropriate solventssuch as dimethyl formamide.

The cyanine dyes defined by Formula II above are conveniently prepared,for example, by heating a mixture of (1) a compound of Formula IV aboveand (2) a compound of the formula:

(VII) wherein D, D R an R are as previously defined, in approximatelyequimolar proportions, in a solvent medium, such as acetic anhydride,containing a strong mineral acid such as perchloric acid. After coolingand diluting with ether, the solid which separates is recrystallized.The preparation of intermediates corresponding to above Formula VII canbe carried out by the general method described 7 in M. Coenen et al.,US. Pat. No. 2,930,694, issued Mar. 29, 1960.

In accordance with the invention, novel and improved direct positivephotographic silver halide emulsions are prepared by incorporating oneor more of the cyanine dyes of the invention into a suitable foggedsilver halide emulsion. The emulsion can be fogged in any suitablemanner, such as by light or with chemical fogging agents, e.g.,stannaous chloride, formaldehyde, thiourea dioxide, and the like. Theemulsion may be fogged by the addition thereto of a reducing agent, suchas thiourea dioxide, and a compound of a metal more electropositive thansilver, such as a gold salt, for example, potassium chloroaurate, asdescribed in British Pat. 723,019 (1955).

Typical reducing agents that are useful in providing such emulsionsinclude stannous salts, e.g., stannous chloride, hydrazine, sulfurcompounds such as thiourea dioxide, phosphonium salts such astetra(hydroxymethyl) phosphonium chloride, and the like. Typical usefulmetal compounds that are more electropositive than silver include gold,rhodium, platinum, palladium, iridium, etc., preferably in the form ofsoluble salts thereof, e.g., potassium chloroaurate, auric chloride, (NHPdCl and the like.

Useful concentrations of reducing agent and metal compound (e.g., metalsalt) can be varied over a considerable range. As a general guideline,good results are obtained using about .05 to 40 mg. reducing agent permole of silver halide and 0.5 to 15.0 mg. metal compound per mole ofsilver halide. Best results are obtained at lower concentration levelsof both reducing agent and metal compound.

The concentration of added dye can very widely, e.g., from about 50 to2000 mg. and preferably from about 400 to 800 mg. per mole of silverhalide in the direct positive emulsions.

As used herein, and in the appended claims, fogged refers to emulsionscontaining silver halide grains which produce a density of at least 0.5when developed, without exposure, for 5 minutes at 68 F. in developerKodak DK-SO having the composition set forth below, when the emulsion iscoated at a silver coverage of 50 mg. to 500 mg. per square foot.

DEVELOPER G. N-methyl-p-aminophenol sulfate 2.5 Sodium sulfite(anhydrous) 30.0 Hydroquinone 2.5 Sodium metaborate 10.0 Potassiumbromide 0.5

Water to make 1.0 l.

The dyes of this invention are also advantageously incorporated indirect positive emulsions of the type in which a silver halide grain hasa water-insoluble silver salt center and an outer shell composed of afogged waterinsoluble silver salt that develops to silver Withoutexposure. The dyes of the invention are incorporated, preferably, in theouter shell of such emulsions. These emulsions can be prepared invarious ways, such as those described in Berriman US. patent applicationSer. No. 448,467, filed Apr. 15, 1965, now US. Pat. 3,367,778 issuedFeb. 6, 1968. For example, the shell of the grains in such emulsions maybe prepared by precipitating over the core grains a light-sensitivewater-insoluble silver salt that can be fogged and which fog isremovable by bleaching. The shell is of sufiicient thickness to preventaccess of the developer used in processing the emulsions of theinvention to the core. The silver salt shell is surface fogged tomake itdevelopable to metallic silver with conventional surface imagedeveloping compositions. The silver salt of the shell is sufficientlyfogged to produce a density of at least about 0.5 when developed for 6minutes at 68 F. in Developer A below when the emulsion is coated at a 8silver coverage of 100 mg. per square foot. Such fogging can be effectedby chemically sensitizing to fog with the sensitizing agents describedfor chemically sensitizing the core emulsion, high intensity light andthe like fogging means well known to those skilled in the art. While thecore need not be sensitized to fog, the shell is fogged. Fogging bymeans of a reduction sensitizer, a noble metal salt such as gold saltplus a reduction sensitizer, a sulfur sensitizer, high pH and low pAgsilver halide precipitating conditions, and the like can be suitablyutilized. The shell portion of the subect grains can also be coatedprior to fogging.

DELEVOPER A G. N-methyl-p-arninophenol sulfate 2.5 Ascorbic acid 10.0Potassium metaborate 35.0 Potassium bromide 1.0

Water to 1 liter. pH of 9.6.

Before the shell of water-insoluble silver salt is added to the silversalt core, the core emulsion is first chemically or physically treatedby methods previously described in the prior art to produce centerswhich promote the deposition of photolytic silver, i.e., latent imagenucleating centers. Such centers can be obtained by various techniquesas described herein. Chemical sensitization techniques of the typedescribed by Antoine Hautot and Henri Sauvenier in Science et IndustriesPhotographiques, Vol. XXVIII, January 1957, pages 1 to 23 and January1957, pages 57 to are particularly useful. Such chemical sensitizationincludes three major classes, namely, gold or noble metal sensitization,sulfur sensitization, such as by a liabile sulfur compound, andreduction sensitization, e.g., treatment of the silver halide with astrong reducing agent which introduces small specks of metallic silverinto the silver salt crystal or grain.

The dyes of this invention are highly useful electron acceptors in highspeed direct positive emulsions comprising fogged silver halide grainsand a compound which accepts electrons, as described and claimed inIllingsworth US. patent application Ser. No. 609,794, filed Jan. 17,1967, and titled Photographic Reversal Materials III," andcontinuation-in-part application Ser. No. 619,936 filed Mar. 2, 1967,now US. Pat. 3,501,307 issued Mar. 17, 1970. The fogged silver halidegrains of such emulsions are such that a test portion thereof, whencoated as a photographic silver halide emulsion on a support to give amaximum density of at least about one upon processing for six minutes atabout 68 F. in Kodak DK-SO- developer, has a maximum density which is atleast about 30% greater than the maximum density of an identical coatedtest portion which is processed for six minutes at about 68 F. in KodakDK-SO developer after being bleached for about 10 minutes at about 68 F.in a bleach composition of:

Potassium cyanide mg 50 Acetic acid (glacial) cc 3.47 Sodium acetate g11.49 Potassium bromide mg 119 Water to 1 liter.

The grains of such emulsions will lost at least about 25% and generallyat least about 40% of their fog when bleached for ten minutes at 68 F.in a potassium cyanide bleach composition as described herein. This fogloss can be illustrated by coating the silver halide grains as aphotographic silver halide emulsion on a support to give a maximumdensity of at least 1.0 upon processing for six minutes at about 68 F.in Kowak DK-50 developer and comparing the density of such a coatingwith an identical coating which is processed for six minutes at 68 F. in

Kodak DK-50 developer after being bleached for about minutes at 68 F. inthe potassium cyanide bleach composition. As already indicated, themaximum density of the unbleached coating will be at least greater,generally at least 60% greater, then the maximum density of the bleachedcoating.

The silver halides employed in the preparation of the photographicemulsions useful herein include any of the photographic silver halidesas exemplified by silver bromide, silver iodide, silver chloride, silverchlorobromide, silver bromoiodide, silver chlorobromide, and the like.Silver halide grains having an average grain size less than about onemicron, preferably less than about 0.5 micron, give particularly goodresults. The silver halide grains can be regular and can be any suitableshape such as cubic or octahedral, as desscribed and claimed inIllingsworth U.S. patent application Ser. No. 609,778, filed Jan. 17,1967, and titled Direct Positive Photographic Emulsions I, andcontinuation-in-part application Ser. No. 619,909 filed Mar. 2, 1967,now U.S. Pat. 3,501,306 issued Mar. 17, -1970. Such grainsadvantageously have a rather uniform diameter frequency distribution, asdescribed and claimed in Illingsworth U.S. patent application Ser. No.609,790, filed Jan. 17, 1967, and titled Photographic Reversal EmulsionsII, and continuationin-part application Ser. No. 619,948 filed Mar. 2,1967, now U.S. Pat. 3,501,305 issued Mar. 17, 1970. For example, atleast 95%, by weight, of the photographic silver halide grains can havea diameter which is within about preferably within about 30% of the meangrain diameter. Mean grain diameter, i.e., average grain size, can bedetermined using conventional methods, e.g., as shown in an article byTrivelli and Smith entitled Empirical Relations Between Sensitometricand Size-Frequency Characteristics in Photographic Emulsion Series inThe Photographic Journal, vol. LXXIX, 1949, pages 330-338. The foggedsilver halide grains in these direct-positive photographic emulsions ofthis invention produce a density of at least 0.5 when developed withoutexposure for five minutes at 68 F. in Kodak DK-50 developer when such anemulsion is coated at a coverage of 50 to about 500 mg. of silver persquare foot of support. The preferred photographic silver halideemulsions comprise at least 50 mole percent bromide, the most preferredemulsions being silver bromoiodide emulsions, particularly thosecontaining less than about ten mole percent iodide. The photographicsilver halides can be coated at silver coverages in the range of about50 to about 500 milligrams of silver per square foot of support.

In the preparation of the above photographic emulsions, the dyes of theinvention are advantageously incorporated in the washed, finished silverhalide emulsion and should, of course, be uniformly distributedthroughout the emulsion. The methods of incroporating dyes and otheraddenda in emulsions are relatively simple and Well known to thoseskilled in the art of emulsion making. For example, it is convenient toadd them from solutions in appropriate solvents, in which case thesolvent selected should be completely free from any deleterious effecton the ultimate light-sensitive materials. Methanol, isopropanol,pyridine, water, etc., alone or in admixtures, have proven satisfactoryas solvents for this purpose. The type of silver halide emulsions thatcan be sensitized with the new dyes include any of those prepared withhydrophilic colloids that are known to be satisfactory for disperingsilver halides, for example, emulsions comprising natural materials suchas gelatin, albumin, agar-agar, gum arabic, alginic acid, etc. andhydrophilic synthetic resins such as polyvinyl alcohol, polyvinylpyrrolidone, cellulose ethers, partially hydrolyzed cellulose acetate,and the like.

The binding agents for the emulsion layer of the photographic elementcan also contain dispersed polymerized vinyl compounds. Such compoundsare disclosed, for example, in U.S. Pats. 3,142,568; 3,193,386;3,062,674 and 3,220,844 and include the water insoluble polymers ofalkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates ormethacrylates and the like.

The dyes, reducing agents and metal compounds of the invention can beused With emulsions prepared, as indi cated above, with any of thelight-sensitive silver halide salts including silver chloride, silverbromide, silver chlorobromide, silver bromoiodide, silverchlorobromoiodide, etc. Particularly useful are direct positive foggedemulsions in which the silver salt is a silver bromohalide comprisingmore than 50 mole percent bromide. Certain dyes of this invention arealso useful is emulsions which contain color formers.

The novel emulsions of this invention may be coated on any suitablephotographic support, such as glass, film base such as celluloseacetate, cellulose acetate butyrate, polyesters such as poly(ethyleneterephthalate), paper, baryta coated paper, polyolefin coated paper,e.g., polyethylene or polypropylene coated paper, which maybe electronbombarded to promote emulsion adhesion, to produce the novelphotographic elements of the invention.

The invention is further illustrated by the following examples.

EXAMPLE 1 l,3-diethyl-6'-nitro-3 -pyrrolo [2,3-b]quinoxalinothiacarbocyanine p-toluenesulfonate 0.115 osotclrn 1 ethyl 3formylpyrrolo[2,3-b]quinoxaline (0.56 g., 1 mol.) and3-ethyl-2-methyl-6-nitrobenzothiazolium ptoluenesulfonate (0.99 g., 1mol.) in acetic anhydride (10 ml.) are heated at reflux for 1 minute.The cooled solution is slowly diluted with excess ether and the solidwhich is precipitated is collected and washed with ether. After onerecrystallization from methtanol, the yield of purified dye is 0.77 g.(51%), M.P. 281-282 C., dec.

The above prepared dye containing the desensitizing 3-ethyl-6-nitrobenzothiazole nucleus is photographically tested for itsusefulness as an electron acceptor and spectral sensitizer for foggeddirect positive photographic silver halide emulsions by the followingprocedure.

A gelatin silver bromoiodide emulsion (2.5 mole per cent of the halidebeing iodide) and having an average grain size of about 0.2 micron isprepared by adding an aqueous solution of potassium bromide andpotassium iodide, and an aqueous solution of silver nitrate,simultaneously to a rapidly agitated aqueous gelatin solution at atemperature of 70 C., over a period of about 35 minutes. The emulsion ischill-set, shredded and Washed by leaching with cold water in theconventional manner. The emulsion is reduction-gold fogged by firstadding 0.2 mg. of thiourea dioxide per mole of silver and heating for 60minutes at 65 C. and then adding 4.0 mg. of potassium chloroaurate permole of silver and heating for 60 minutes at 65 C. The dye of the aboveexample, 1,3 diethyl 6'nitro-3-pyrrolo[2,3-b]quinoxalinothiacarbocyanine p-toluenesulfonate, isthen added to the above fogged emulsion in amount sufiicient to give aconcentration of 0.08 gram of the dye per mole of silver. The resultingemulsion is coated on a cellulose acetate film support at a coverage ofmg. of silver and 400 mg. of gelatin per square foot of support.

A sample of the coated support is then exposed on an Eastman Ibsensitometer using a tungsten light source and processed for 6 minutesat room temperature in Kodak D-19 developer which has the followingcomposition:

Water to make 1.0 liter.

then fixed, washed and dried. The results are listed in Table Ihereinafter. Referring thereto, it will be seen that the dye of thisexample has a maximum density in the unexposed areas of 1.63 and aminimum density in exposed areas of 0.06, a maximum sensitivity of 550nm. and a relative speed of 380. This result indicates that the dyecompound of the above example is Well suited to function as both anelectron acceptor and spectral sensitizer. It thus provides excellentquality direct positive photographic silver halide emulsions. Excellentmagenta images are obtained when the color former1-(2,4,6-trichlorophenyl) 3{3-[(2,4-di-tert-pentylphenoxy)acetamido]-benzamido}-2-pyrazolin-5-oneis incorporated in the emulsion of this example, the emulsion is coatedon a support, exposed to a tungsten source through Wratten filter No. 61and No. 16, and reversal processed as described in Graham et al. US.Pat. 3,046,129, issued July 24, 1962, in Example (a) col., 27, lines 27et seq. except that black-and-white (MQ) development is omitted, thecolor development is reduced to one minute and is conducted in totaldarkness until after fixing.

In place of the 3-ethyl-2-methyl-6-nitrobenzothiazoliump-toluenesulfonate in the above example, there can be substituted anequivalent amount of any other of the intermediates defined by FormulaIII above to give the corresponding other cyanine dyes of the inventionhaving generally similar properties as electron acceptors and spectralsensitizers for photographic silver halide emulsions, and moreparticularly for direct positive photographic emulsion, for example, thedye 1',3-diethyl-6- nitrooxa 3'-pyrro1o[2,3-b]quinoxalinocarbocyaninesalt (e.g., the chloride, bromide, iodide, perchlorate,p-toluenesulfonate, etc. salt); the dye 1,3-diethyl-6'-nitro-3-pyrrolo-[2,3-b]quinoxalinoselenacarbocyanine salt (e.g., the chloride, bromide,iodide, perchlorate, p-toluenesulfonate, etc. salts); and the likecyanine dyes.

EXAMPLE 2 1,3 diallyl-1'-ethylimidazo [4,5-b] quinoxalino-3'-pyrrolo-[2,3-b] quinoxalinocarbocyanine p-toluenesulfonate l CHrCH=CH2 Thiscompound is prepared and isolated by the same procedure as thatdescribed for Example 1, except that 1,3diallyl-Z-methylimidazo[4,5-b]quinoxalinium p-toluenesulfonate (1.09 g.,1 mol.) is used instead of 3-ethyl- 2 methyl 6 nitrobenzothiazoliump-toluenesulfonate. After two recrystallizations from methanol, theyield of of purified dye is 0.28 g. (17%), M.P. 250252 C. dec.

The above prepared dye containing the desensitizing 1,3diallylimidazo[4,5-b]-quinoxaline nucleus is photographically tested bythe procedure described in above Example 1. The results are recorded inTable 1 hereinafter. Reference thereto indicates that this dye is anexcellent electron acceptor and spectral sensitizer for fogged directpositive photographic emulsions. The densities are 1.30 and 0.02 for theunexposed and exposed areas, re-

12 V spectively, with a maximum sensitivity at 538 nm. and a relativespeed of 912.

EXAMPLE 3 1'-ethyl-'1, 3 3-trimethyl-3H-pyrrolo 2,3 -b] pyrido-3pyrrolo[2,3-b]quinoxalinocarbocyanine iodide 1 ethyl3-formylpyrrolo[2,3-b]quinoxaline (0.56 g., 1 mol.),1,3,3-trimethyl-2-methylene-2,3-dihydropyrrolo- [2,3-b]pyridine (0.44g., 1 mol.) and p-toluenesulfonic acid monohydrate (0.48 g., 1 mol.) inacetic anhydride (10 ml.) are heated at reflux for 1 minute. When cool,the mixture is diluted with excess ether and the product separated as anoil. The oil is dissolved in boiling methanol ml.) containing 47%aqueous HI (1.25 ml.). The solution is filtered, then chilled. The solidwhich crystallizes is collected and after a further recrystallizationfrom methanol, the yield of purified dye is 0.38 g. (26% M.P.indistinct.

This dye containing the desensitizing 1,3,3-trimethyl-3H-pyrrolo[2,3-b]pyridine nucleus is tested in accordance 'with the testprocedure of Example 1. The results of the test are recorded in Table 1hereinafter. The densities are 1.65, and 0.03 for the unexposed andexposed areas, respectively, with maximum sensitivity at 530 nm. and arelative speed of 708. Accordingly, this dye is an excellent electronacceptor and spectral sensitizer for fogged direct positive photographicemulsions.

EXAMPLE 4 6-chloro-1'-ethyl 1,3 diphenylimidazo[4,5-b]quinoxalino 3'pyrrolo[2,3-b]quinoxalinocarbocyanine ptoluenesulfonate This dye isprepared and purified in the same manner as that described for Example2, except that 6-chl0ro-2 methyl-1,3 diphenylimidazo[4,5-b]quinoxaliniump-toluenesulfonate (1.36 g., 1 mol.) is used in place of 1,3-diallyl-Z-methylimid-azo[4,5-b]quinoxalinium p toluenesulfonate. Theyield of purified dye is 0.21 .g. (11%), M.P. 300 C.

The above prepared dye containing the desensitizing1,3-diphenylimidazo]4,5-b]quinoxaline nucleus is tested by theproducedure described in above Example 1. Reference thereto indicatesthat is dye is an outstanding electron acceptor and spectral sensitizerfor fogged direct positive photographic emulsions. The densities are1.64 and 0.02 for the unexposed and exposed areas, respectively, withmaximum sensitivity at 550 nm. and a relative speed of 891.

13 EXAMPLE 1'-ethyl-1,3,3-trimethyl-5-nitroindo-3 '-pyrrolo [2,3-b]quinoxalinocarbocyanine p-toluenesulfonate H OS 0207117 This dye isprepared and purified in the same manner as that described for Example2, except that 1,2,3,3-tetramethyl-5nitro-3H-indolium p-toluenesulfonate(0.98 g., 1 mol.) is used in place of 1,3-diallyl2-methylimidazo-[4,5-b]quinoxalinium p-toluenesulfonate. The yield of purified dye is0.56 g. (38%), MP. 257-258 C., dec.

This dye containing the desensitizing 1,3,3-trimethyl- 5-nitro-3H-indolenucleus is tested in accordance with the test procedure of aboveExample 1. The results are recorded in Table 1 hereinafter. Referring tothe table, it will be seen that the densities are 1.64 and 0.10 for theunexposed and exposed areas, respectively, with maximum sensitivity at550 nm. and a relative speed of 661. This dye is accordingly, anexcellent electron acceptor and spectral sensitizer for fogged directpositive photographic emulsions.

EXAMPLE 6 1-butyl-7chloro-3'-ethyl-6'-nitro-3-pyrrolo 2,3-b]quinoxalinothiacarbocyanine p-toluenesulfonate This dye is prepared inthe same manner as Example 1, except that1-butyl-7-chloro-3-formylpyrrolo[2,3-b1quinoxaline (0.72 g., 1 mol.) isused in place of 1-ethyl-3- formylpyrrolo[2,3-b]quinoxaline. After tworecrystallizations from methanol, the yield of purified dye is 0.85 g.

(51%), MP. 2489 C., dec.

The above prepared dye containing the desensitizing1-ethyl-6-nitrobenzothiazole nucleus is an excellent electron acceptorand spectral sensitizer for fogged photographic reversal emulsions asindicated by the test procedure of above Example 1, the results of whichare recorded in Table 1 hereinafter. The densities are 1.82 and 0.05 forthe unexposed and exposed areas, respectively, with a maximumsensitivity at 535 nm. and a relative speed of 692.

EXAMPLE 7 1,3-diallyll-butyl-7'-chloroimidazo [4,5 -b] quinoxaline-3-pyrrolo [2,3-b] quinoxalinocarbocyanine bromide Q more...

/ l N N N N v omwHmN CH=CH-\ l Er e CHgCH=CHg The dye is prepared in thesame manner as Example 2, except that1-butyl-7-chloro-3-formylpyrrolo[2,3-b]quin oxaline (1.09 g., 1 mol.) isused in place of 1-ethyl-3- for-mylpyrrolo[2,3-b]quinoxaline. After tworecrystallizations from methanol containing HBr, the yield of purifieddye is 0.72 g. (46%), MP. 2068 C., dec.

The above prepared dye containing the desensitizing1,3-diallylimidazo[4,5-b]quinoxaline nucleus is tested by the procedureof Example 1. The results are recorded in Table 1 hereinafter. Referringthereto, the densities are 1.90 and 0.03 for the unexposed and exposedareas, respectively, with maximum sensitivity at 530 nm. and a relativespeed of 955. This dye is, accordingly, an excellent electron acceptorand spectral sensitizer for fogged direct positive photographicemulsions.

EXAMPLE 8 1-b11tyl-7'-chloro- 1 ,3 ,3-trimethyl-5-nitroindo-3 -pyrrolo-[2,3-b] quinoxalinocarbocyanine bromide CH CH3 N N NO2 CH CH N CH=CHThis dye is prepared in the same manner as Example 5, except that1-buty1-7-chloro-3-formylpyrrolo[2,3-b] quinoxaline (0.72 g., 1 mol.) isused in place of 1-ethyl- 3-formylpyrrolo[2,3-b]quinoxaline. After tworecrystal lizations from methanol containing HBr, the yield of purifieddye is 0.71 g. (53%), MP. 24850 C., dec.

This dye containing the desensitizing 1,3,3-trimethyl- 5-nitro-3H-indolenucleus is an excellent electron acceptor and spectral sensitizer forfogged direct positive photographic emulsions as indicated by the testprocedure of above Example 1, the results of which are recorded in Table1 hereinafter. The densities are 1.86 and 0.04 for the unexposed andexposed areas, respectively, with maximum sensitivity at 548 nm. and arelative speed of 661.

The following Examples 9 to 14 illustrate the preparation of cyaninedyes of the invention wherein R of Formula I above is an arylsubstituent. The results obtained with these dyes by the testingprocedure of above Example 1 are listed in Table 1 hereinafter.

EXAMPLE 9 3 '-ethyl- 1-methyl-6'-nitro-2-p-tolyl-3 -pyrrolo [2,3-b]quinoxalinothiacarbocyanine p-toluenesulfonate 8 N02 CHa-N %CH=CH l6030107111 3 formyl-1-methy1-2-p-tolylpyrrolo[2,3-b1quin0xa1ine (0.75g., 1 mol.) and 3-ethyl-2-methyl-6-nitrobenzothiazoliump-toluenesulfonate (0.99 g., 1 mol.) in acetic anhydride (10 ml.) isheated at reflux, with constant stirring, for 1 minute. The mixture isallowed to cool and solid separated. Ether is added and the solidcollected and washed with ether. After recrystallization from methanolacidified with a little p-toluenesulfonic acid, the yield of purifieddye is 1.34 g. (79%) MP. 261-3" 0., (dec.).

15 EXAMPLE 10 1,3-diallyl-l-methyl 2 ptolylimidazo[4,5-b]quinoxalino-3-pyrrolo[2,3 -b]quinoxalinocarbocyaninep-toluenesulfonate This dye is prepared and purified in the same manneras that described in Example 9, except that 1,3-diallyl-2-methylimidazo[4,5 b]quinoxalinium p-toluenesulfonate (1.09 g., 1 mol.)is used in place of 3-ethyl-2-methyl-6- nitrobenzothiazoliump-toluenesulfonate. The yield of purified dye is 1.28 g. (71%), M.P. 269C., (dec.).

EXAMPLE ll 6 chloro-l'-methyl-1,3-diphenyl-2-p-tolylimidazo [4,5-b]quinoxalino 3' pyrrolo[2,3 b]quinoxalinocarbocyanine p-toluenesulfonateEXAMPLE 12 1,1,3,3-tetramethyl-5-nitro-2-p-tolylindo-3'-pyrro1o-[2,3-b]quinoxalinocarbocyanine p-toluenesulfonate -NO2 e CHN CH=CH S CH3 0 2 1 1 This dye is prepared and purified in the same manner as thatdescribed in Example 9, except that1,2,3,3-tetramethyl-S-nitro-3H-ind0lium p-toluenesulfonate (0.98 g., 1mol.) is used in place of 3-ethyl-2-rnethyl-6-nitrobenzothiazoliump-toluenesulfonate. The yield of purified dye is 0.78 g. (46%), M.P.1868 C., (dec.).

CH3 CH 1 6 EXAMPLE 13 1 ,1',3 ,3-tetramethyl-2-p-tolylpyrrolo [2,3-b]pyrido-3 pyrrolo [2,3 -b] quinoxalinocarbocyanine perchlorate CH3 CH3This dye is prepared in the same manner as that described in Example 9,except that l,2,3,3-tetramethyl-3H- pyrrol0[2,3-b]pyridiniump-toluenesulfonate (0.89 g., 1 mol.) is used in place of3-ethyl-2-methyl-6-nitrobenzothiazolium p-toluenesulfonate. The yield ofpurified dye is 0.88 g. (63% M.P. 295 C. (dec.) after recrystallizationfrom methanol containing perchloric acid.

EXAMPLE 14 1,1'-dimethyl-2,8-diphenyl-2'-p-tolyl-3-indolo-3 -pyrrolo-[2,3-b]quinoxalinocarbocyanine perchlorate 3formyl-1-methyl-2-p-tolylpyrrolo[2,3-b]quinoxaline (0.75 g., 1 mol.) and1-methyl-3-methylenebenzyl-2- phenylindole (0.77 g., 1 mol.) are addedto a solution of 72% perchloric acid (0.28 g.) in acetic anhydride (10ml.). The mixture is heated on a steam bath for 15 minutes, as greencrystals separate. The mixture is allowed to cool, diluted with a littleether, and the solid collected. After recrystallization from aceticacid, the yield of purified dye is 1.04 g. (60%) M.P. 225 C. (dec.).

In place of the 1-methyl-3-methylenebenzyl-2-phenylindole in the aboveExample 14, there can be substituted an equivalent amount of, forexample, 1-methyl-3-rnethylenebenzyl-Z-p-tolylpyrrolo[2,3-b]quinoxalineto give the corresponding dye having generally similar properties as anelectron acceptor and spectral sensitizer for direct positivephotographic silver halide emulsions.

The following Examples 15 to 20 illustrate the preparation of cyaninedyes of the invention containing the l-aryl- 3-pyrrolo[2,3-b]pyrazinenucleus, i.e., wherein R and R of Formula I each represent hydrogen,alkyl, or aryl. The results obtained with these dyes by the testingprocedure described in above Example 1 are recorded in Table 1hereinafter.

EXAMPLE 15 A mixture of 1.12 g. (1 mol.) of3-formyl-1-phenylpyrrolo[2,3-b]pyrazine, 1.98 g. (1 mol.) of 3-ethyl-2-methyl-6-nitrobenzothiazoliurn p-toluenesulfonate, and 10 ml. of aceticanhydride are heated at reflux for 2 minutes. After chilling, the crudedye is collected on a filter and washed first with acetic anhydride,then with ether. After two recrystallizations from acetic acid, 2.47 g.(87%) of pure dye is obtained as shiny orange plates, M.P. 200- 202 C.,(dec.).

EXAMPLE 16 3-methyl-5-nitro-1'-phenyloxa-3 '-pyrrolo [2,3-b]pyrazinocarbocyanine ptoluenesulfonate A mixture of 1.12 g. (1 mol.) of3-formy1-1-phenylpyrrolo[2,3-b]pyrazine, 1.82 g. (1 mol.) of2,3-dimethy1- -nitrobenzoxazolium p-toluenesulfonate, and ml. of aceticanhydride are heated at reflux for 2 minutes. The solution is chilledand diluted with 50 ml. of ether. The crude dye is collected on a filterand washed with ether. After recrystallization from acetic acid, 1.16 g.(54%) of pure dye is obtained as bright yellow crystals, M.P. 232-235 C.(dec.).

EXAMPLE 17 1,3-dimethyl- 1'-phenylimidazo [4,5 -b] quinoxalino-3 pyrrolo2,3-b] pyrazinocarbocyanine p-toluenesulfonate A mixture of 1.12 g. (1mol.) of 3-formyl-1-phenylpyrrolo[2,3-b]pyrazine, 1.92 g. (1 mol.) of1,2,3-trirnethylirnidazo[4,5-b1quinoxalinium p-toluenesulfonate and 10ml. of acetic anhydride is heated at reflux for a minute. Afterchilling, the crude dye is collected on a filter and Washed first withacetic anhydride and then with ether. After recrystallization fromacetic acid, 1.0 g. (34%) of pure dye is obtained as rust crystals, M.P.281-285 C. (dec.).

EXAMPLE 18 6-chloro-1,1',3 -triphenylirnidazo [4,5 -b] quinoxalino-3pyrrolo [2,3 -b] pyrazinocarbocyanine bromide A mixture of 1.12 g. (1mol.) of 3-formyl-1-phenylpyrrolo[2,3-b]pyrazine, 2.72 g. (1 mol.) of6-chloro-2- methyl-1,3-diphenylimidazo [4,5-b] quinoxalinium ptoluenesulfonate, and m1. of acetic anhydride is heated at reflux for 2minutes. After chilling, the solution is diluted with 300 ml. of etherand the resultant solid, which proved to be very hydroscopic, iscollected rapidly on a filter. The solid is dissolved in 200 ml. of warmmethyl alcohol and treated with a solution of 1.0 g. (2 mols.) of sodiumbromide in 10 ml. of water. The crude dye is collected on a filter andwashed first with methyl alcohol, and then with water. After stirring in100 ml. of hot methyl alcohol and filtering while hot, 0.93 g. (28%) ofpure dye is obtained as a dull yellow powder, M.P. 300: C.

18 EXAM'PLE 19 1 ,3 ',3 '-trimethyl-1-phenyl-3 -pyrrolo [2,3-bpyrazino-3 H- pyrrolo [2,3 -b] pyridocarbocyanine p-toluenesulfonate Amixture of 1.12 g. (1 mol.) of S-formyl-l-phenylpyrrolo[2,3-b]pyrazine,0.87 g. (1 mol.) of 1,3,3-trimethyl-2-methylene-2,3-dihydropyrrolo[2,3b]pyridine, 1.0 g. (1 mol.) of p-toluenesulfonic acid monohydrate and 10ml. of acetic anhydride are heated at reflux for 2 minutes. Afterchilling, 350 ml. of ether are added, and the viscous oil is separatedfrom the supernatant liquid by decantation. The oil is stirred with 100ml. of ether which induced crystallization. The crude dye is collectedon a filter, and washed with ether. After recrystallization, first frommethyl alcohol-toluene and then from dioxane, 0.26 g. (9%) of pure dyeis obtained as brown crystals, M.P. 206-210" C. (dec.).

EXAMPLE 20 1,3 ,3-trimethyl-5-nitro-1-phenylindo-3 -pyrrolo [2,3 -b]pyrazino-carbocyanine p-toluenesulfonate w on. 011

-No. C ll -N -011=on N CH. OSOzC7H7 A mixture of 1.12 g. (1 mol.) of3-formy1-1-phenylpyrrolo[2,3-b]pyrazine, 1.95 g. (1 mol.) of1,2,3,3-tetramethyl-5-nitro-3I I-indolium p-toluenesulfonate, and 10 ml.of acetic anhydride is heated at reflux for 2 minutes. After chilling 20ml. of ether are added. The crude dye is collected on a filter andwashed with ether. Two recrystallizations from acetic acid yields 1.57g. (53%) of pure dye as bright orange crystals, M.P. 255 C. (dec.).

The effectiveness of the dyes of the invention as electron acceptors andspectral sensitizers for fogged direct positive photographic silverhalid emulsions, as determined by the exact testing procedure describedin above Example 1, is recorded in the following table.

TABLE 1 Density Dye Rela- Sensic0nc., tive Max. unmin. extivity g./moleclear exposed posed max. Dye of Example No. silver speed areas areas(nm.)

None 1 1. 90 N0 reversal It will be noted from the above Table I thatExamples 9 to 14, wherein R of Formula I above is an aryl substituent,show very good reversals and outstanding relative speeds ranging from1050 to 1620, with maximum sensitivity at from 540 to 650 nm. Examples 1to 8 and 15 to 20 also show excellent reversal properties together withgood speeds and desirable sensitivity maximums. In comparison with theabove results, the control sample containing no dye shows a relativespeed of less than 1 with no reversal indicated.

The following examples further illustrate the preparation of fogged,direct positive photographic emulsions and elements with the cyaninedyes of the invention.

EXAMPLE 21 To 9.0 pounds of a silver chloride gelatin emulsioncontaining an equivalent of 100 grams of silver nitrate is added 0.017gram of 6-chloro-1'-ethy11,3-diphenylimidazo [4,5-b]quinoxalino 3'pyrrolo[2,3-b]quinoxalinocarbocyanine p-toluenesulfonate (Example 4).The emulsion is coated on a non-glossy paper support, and is flashedwith White light to give a density of 1.2 when developed in thefollowing developer, diluted 1 part to 2 parts of water:

Grams N-methyl-p-aminophenol sulfate 3.1 Sodium sulfite, des. 45Hydroquinone 12 Sodium carbonate, des. 67.5 Potassium bromide 1.9 Waterto 1 liter.

The light fogged material can be exposed to an image with lightmodulated by a Wratten No. 15 filter to give a direct positive image.Generally similar results are obtained when the dyes of Example 2, 10and 15 are used in place of the above dye.

EXAMPLE 22 Seven pounds of a silver chloride gelatin emulsion containingthe equivalent of 100 g. of silver nitrate is heated to 40 C. and the pHis adjusted to 7.8. Eight cc. of full strength (40%) formalin solutionis added and the emulsion is held at 40 C. for 10 minutes. At the end ofthe holding period, the pH is adjusted to 6.0 and 0.125 g. of1,3-diallyl-1'-butyl 7'-chloroimidazo[4,5-b]quinoxalino-3'-pyrrolo[2,3-b]quinoxalinocarbocyanine bromide (Example 7). Theemulsion is coated on a support, and provides good direct positiveimages. Similar results are obtained when the dyes of Examples 5, 6, 8and 11 are substituted for the above dye.

The examples which follow illustrate the preparation of a number ofintermediate 1-alkylpyrrolo[2,3-b]quinoxalines employed in the precedingcyanine dye examples.

EXAMPLE A 2-ethylamino-3-methylquinoxaline hydro-p-toluenesulfonate eNH.

2-chloro-3-methy1quinoxaline (35.8 g., 1 mol.) [which may be prepared bythe method of Platt and Sharp, J. Chem. Soc. (1948) 2132], anhydrousethylamine (18.0 g., 1 mol.+100%) and ethanol (200 ml.) are heated at160-175 C. in a autoclave for hours. The mixture is allowed to cool andthe ethanol evaporated under reduced pressure. The product is dissolvedin tetrahydrofuran (200 ml.) and the insoluble material filtered 01f,washed with a little tetrahydrofuran and rejected. The filtrate andwashings are combined and cooled below C. in an ice-bath as a solutionof p-toluenesulfonic acid monohydrate (38.0 g., 1 mol.) intetrahydrofuran is added slow- 1y. The solid which precipitated iscollected and washed with tetrahydrofuran. The yield of buff coloredsolid is 48.8 g. (68%), M.P. l93-195 C. This material is used withoutfurther purification.

20 EXAMPLE B 1-ethyl-3 -formylpyrrolo 2,3 -b] quinoxaline CHO /Ni(\ N N2 ethylamino-3-methylquinoxaline hydro-p-toluenesulfonate (7.18 g., 1mol.) is suspended in dimethylformamide (25 ml.) and triethylamine (2.02g., 1 mol.) is added. The resulting solution is added to a solution ofphosphoryl chloride (9.25 g., 3 mols.) in dimethylformamide (11 ml.) atroom temperature. Some heat is evolved. The mixture is heated on asteam-bath for 3 hours, then poured into water (200 ml.), 5 N NaOH (125m1.) is added and the mixture stirred for 15 minutes. The product isextracted with chloroform, the extract dried over MgSO and thechloroform evaporated. The oily residue, which becomes partiallycrystalline on standing, is stirred with ligroin (50 ml.) and the solidcollected and washed with ligroin. The yield of light grey solid is 1.6g. (30% M.P. 154155 C. This material is used without furtherpurification.

EXAMPLE C 7-chloro-3-methyl-2(1H)-quinoxalinone4-chloro-o-phenylenediamine (71.5 g., 1 mol.) is dissolved in a mixtureof Water (300 ml.) and cone. HCl ml), then pyruvic acid (44.0 g., 1mol.) is added, with stirring. After 1 /2 hrs., the solid is collectedand well washed with Water. After recrystallization fromdimethylformamide/ethanol, the yield is 47.4 g. (49%), M.P. 24850 C.

EXAMPLE D 2,7-dichloro3-methylquinoxaline /N\ CH3 EXAMPLE E1-butyl-7-chloro-3-formylpyrrolo[2,3-b] quinoxaline2,7-dichloro-3-methylquinoxaline (17.1 g., 1 mol.), butylamine (11.7 g.,1 mol.+%) and ethanol (40 ml.) are heated under reflux for 2 hrs. Theethanol is evaporated and the residue is diluted with ether. The solidis filtered off and rejected. Evaporation of the ether gives crude2-butylamino-7-chloro 3 methylquinoxaline, to which is added a warmsolution of phosphoryl chloride (37 g., 3 mol.) in dimethyl formamide(44 ml.). A vigorous reaction occurs. When the reaction subsides, themixture is allowed to cool, then poured in 400 ml. of an ice/watermixture. 5 N NaOH (360 ml.) is added slowly, as more ice is addedperiodically to keep the mixture cool. The aqueous layer is decanted andthe viscous residue digested with ethanol (50 ml.). After chilling, thesolid is collected and washed with ethanol. After one recrystallizationfrom dimethyl formamide, the yield is 4.56 g. (19%), M.P. 169170 C;

EXAMPLE F 2-p-toly1-1H-pyrrolo [2, 3 -b] quinoxaline4-methylimino-2-p-tolyl-2-pyrrolin-5-one hydrochloride (15.4 g., 1 mol.)[which may be prepared by the method of Mumm and Hornhardt. Ber. 70,1930-47 (1937)], ophenylene diamine (7.0 g., 1 mol.) and acetic acid (65ml.) are placed in a flask and heated at reflux for a few seconds, asall the solid dissolved. The mixture is chilled and the solid collectedand washed with ether. The yield is 12.5 g. (74% M.P. 2747 C.

EXAMPLE G 1 -methyl-2p-tolypyrrolo [2,3-b] quinoxaline Sodium hydride(60% in mineral oil, 4.0 g., 1 mol.+ 100%) is placed in a flask fittedwith a thermometer and a stirrer, and protected from atmosphericmoisture. The mineral oil is removed by washing with tetrahydrofuran,followed by decantation. Dimethyl formamide (100 ml.) is added, then2-p-tolyl-1-H-pyrrolo[2,3-b]quinoxaline is added in portions withstirring. When evolution of hydrogen gas has stopped, the flask iscooled in an ice-bath as methyl p-toluenesulfonate (9.05 g., 1 mol.) isadded in portions, keeping the temperature below 20. The mixture isstirred for 4 hours at room temperature.

The mixture is diluted with ice and water, and the solid collected and'well washed with water. After recrystallization from aqueous aceticacid, the yield is 7.45 g. (57%) M.P. 145-6 C.

EXAMPLE H 3-formyl-1-methyl-2-p-tolylpyrrolo [2,3-b] quinoxaline CHO GHQ

Phosphoryl chloride (0.46 g., 1 mol.+50%) is added to dimethylform'amide ml.) and the solution cooled below C.1-methyl-2-p-tolylpyrrolo[2,3-b]quinoxaline (0.55 g., 1 mol.) is added.The mixture is heated on a steam-bath for minutes, cooled, and dilutedwith water ml). 5 N NaOH (4.4 ml.) is added. A viscous mass separatedwhich became crystalline on stirring. The solid is collected and washedwith Water. After recrystallization from ethanol, the yield is 0.40 g.(67%), M.P. 182.5- 183.0 C.

22 EXAMPLE I Z-anilino-3-methyllpyrazine hydro-p-toluenesulfonate Amixture of 51.5 g. (1 mol.) of 2-chloro-3-methylpyrazine and g. (4mols.) of aniline is heated at reflux for 1.5 hours. The mixture iscooled and added to 1 l. of a 10% aqueous potassium carbonate solution.The resultant mixture is extracted three times with 200 ml. portions ofbenzene. The combined organic phase is Washed with water, dried byfiltration through anhydrous magnesium sulfate, and distilled rapidly.The fraction, M.P. l3 6153 C./0.9 mm., is dissolved in 100 ml. oftetrahydrofuran and treated with a solution of excess p-toluenesulfonicacid in 50 ml. of tetrahydrofuran. The resulting solid is collected on afilter, washed with tetrahydrofuran and dried to give 113.8 g. (80%) ofa yellow solid, M.P. 19019 3 C.

EXAMPLE K 3 -formyll -phenylpyrrolo [2,3 -b] pyrazine (IIHO I Ph To apre-formed complex of 11.5 ml. (3 mols.) phosphorus oxychloride in 40ml. of dimethyl formamide is added 17.7 g. (1 mol.) of2-anilino-3-methylpyrazine hydro p-toluenesulfonate. The resultingsolution is heated on a steam bath for 3 hours then poured into 750 ml.of ice water. A 5 N aqueous sodium hydroxide solution is addedportionwise until the solution is strongly basic and the resultantsuspension is heated at 60 C. for 15 minutes. After chilling, the solidis collected on a filter, washed with water and dried. Afterrecrystallization from isopropyl alcohol, 2.98 g. (27%) of product isobtained as a gray fibrous solid, M.P. 176 C.

By substituting other dye compounds of the invention, as defined inFormulas I and II above, into the procedure of the above examples,similar fogged, direct positive photographic silver halide emulsions andphotographic elements may be prepared.

The photographic silver halide emulsion and other layers present in thephotographic elements made according to the invention can be hardenedwith any suitable hardener, including aldehyde hardeners such asformaldehyde, and mucochloric acid, aziridine hardeners, hardeners whichare derivatives of dioxane, oxypolysaccharides such as oxy starch or oxyplant gums, and the like. The emulsion layers can also containadditional additives, particularly those known to be beneficial inphotographic emulsions, including, for example, lubricating materials,stabilizers, speed increasing materials, absorbing dyes, plasticizers,and the like. These photographic emulsions can also contain in somecases additional spectral sensitizing dyes. Furthermore, these emulsionscan contain color forming couplers or can be developed in solutionscontaining couplers or other color generating materials. Among theuseful color formers are the monomeric and polymeric color formers,e.g., pyrazolone color formers, as Well as phenolic, heterocyclic andopen chain couplers having a reactive methylene group. The color formingcouplers can be incorporated into the direct positive photographicsilver halide emulsion using any suitable technique, e.g., techniques ofthe type shown in Jelley et al. US. Pat. 2,322,027, issued June 15,1943, Fierke et al. US. Pat. 2,801,171, issued July 30, 1957, FisherU.S. Pats. 1,055,155 and 1,102,028, issued Mar. 4, 1913, and

June 30, 1914, respectively, and Wilmanns US. Pat. 2,186,849 issued Jan.9, 1940. They can also be developed using incorporated developers suchas polyhydroxybenzenes, aminophenols, 3-pyrazolidones, and the like.

Although the invention has been described in considerable detail withparticular reference to certain preferred embodiments thereof, it willbe understood that variations and modifications can be efiected withinthe spirit and scope of the invention as described hereinabove, and asdefined in the appended claims.

We claim:

1. A fogged direct positive photographic silver halide emulsioncontaining a dye selected from those comprising first and secondnitrogen containing heterocyclic nuclei joined together by a methinelinkage selected from the group consisting of a dimethine linkage and atrimethine linkage; the first of said nuclei being selected from thegroup consisting of a l-alkyl or a l-aryl substitutedpyrrolo[2,3-b]pyrazine nucleus and a l-alkyl or a l-aryl substitutedpyrrolo[2,3-b]quinoxaline nucleus joined at the 3-carbon atom thereof tosaid linkage; and said second nucleus containing from to 6 atoms andbeing selected from the group consisting of (a) a heterocyclic nitrogencontaining nucleus of the type used in cyanine dyes when said linkage isa dimethine linkage; and, (b) when said linkage is a trimethine linkage,said second nucleus is selected from the group consisting of a2-arylindole nucleus, 2. l-alkyl or a l-aryl substituted pyrrolo[2,3-b]quinoxaline nucleus and a l-alkyl or a l-aryl substitutedpyrrolo[2,3-b]pyrazine nucleus, each of said nuclei being joined at the3-carbon atom thereof to said trimethine linkage.

2. A direct positive emulsion in acordance with claim 1 containing aphotographic color coupler dispersed in coupler solvent.

3. A direct positive, photographic emulsion in accord ance with claim 1wherein at least 95%, by weight, of said silver halide grains have asize which is within about 40% of the average grain size.

4. A direct positive emulsion as defined by claim 1 wherein said secondnucleus is a desensitizing nucleus.

5. A direct positive emulsion as defined by claim 1 wherein said secondnucleus is a nitro substituted desensitizing nucleus.

6. A direct positive emulsion as defined by claim 1 wherein said secondnucleus is an imidazo[4,5-b]quinoxaline desensitizing nucleus.

7. A direct positive emulsion as defined by claim 1 wherein said secondnucleus is a 1,3,3-trialkyl-3H-pyrrolo[2,3-b]pyridine desensitizingnucleus.

8. A direct positive emulsion as defined by claim 1 wherein said secondnucleus is a 2-arylindole nucleus.

9. A direct positive emulsion in accordance with claim 1 in which thesaid silver halide is present in the form of chemically fogged silverhalide grains.

10. A direct positive emulsion in accordance with claim 1 in which thesaid silver halide is present in the form of reduction and gold foggedsilver halide grains.

11. A direct positive, photographic emulsion in accordance with claim 1which comprises fogged silver halide grains, said grains being such thata test portion thereof, when coated as a photographic silver halideemulsion on a support to give a maximum density of at least about 1 uponprocessing for 6 minutes at about 68 F. in Kodak DK-SO developer has amaximum density which is at least about 30% greater than the maximumdensity of an identical coated test portion which is processed for 6minutes at about 68 F. in Kodak DK-SO developer after being bleached forabout minutes at about 68 F. in a bleach composition of:

Potassium cyanide mg 50 Acetic acid (glacial) cc 3.47 Sodium acetate g11.49 Potassium bromide mg 119 Water to 1 liter.

12. A fogged direct positive photographic silver halide emulsioncontaining at least one cyanine dye selected from those represented bythe following general formulas:

and

wherein n represents a positive integer of from 1 to 2; L represents amethine linkage; R represents a member selected from the groupconsisting of an alkyl group, an alkenyl group and an aryl group; Rrepresents a member selected from the group consisting of an alkyl groupand an aryl group; R and R each taken individually represents a memberselected from the group consisting of a hydrogen atom, an alkyl group,and an aryl group; R and R taken together represent the non-metallicatoms necessary to complete a pyrrolo[2,3-b]quinoxaline nucleus; Rrepresents a member selected from the group consisting of a hydrogenatom and an aryl group; R represents a member selected from the groupconsisting of an alkyl group, an aryl group and a heterocyclic radicalcontaining from 5 to 6 atoms in the heterocyclic ring and having ahetero nitrogen, oxygen or sulfur atom; X represents an acid anion; Drepresents the non-metallic atoms necessary to complete a nucleusselected from the group consisting of a 2-arylindole nucleus, apyrrolo[2,3-b]pyrazine nucleus and a pyrrol0[2,3-b]quinoxaline nucleus;and Z represents the non-metallic atoms necessary to complete a nitrogencontaining heterocyclic nucleus of the type used in cyanine dyescontaining from 5 to 6 atoms in the heterocyclic ring.

13. A direct positive emulsion in accordance with claim 12 wherein saidZ of said dye represents the nonmetallic atoms required to complete adensitizing nucleus.

14. A direct positive emulsion in accordance with claim 12 wherein saidZ represents the non-metallic atoms required to complete a densitizingnucleus selected from the group consisting of a nitrobenzothiazole nucleus, a nitrobenzoxazole nucleus, a nitrobenzoselenazole nucleus, anitroindole nucleus, an imidaZo[4,5-b]quinoxaline nucleus, and al,3,3,trialkyl-3H-pyrrolo[2,3-b]pyridine nucleus.

15. A direct positive emulsion as defined by claim 12 wherein said R andR of said dye each represents a hydrogen atom.

16. A direct positive emulsion as defined by claim 12 where said R and Rof said dye taken together represent the non-metallic atoms necessary tocomplete a pyrrolo [2,3-b] quinoxaline nucleus.

17. A direct positive emulsion'as defined by claim 12 wherein saidcyanine dye is selected from the group consisting of1,3-diethyl-6-nitro-3-pyrrolo [2,3-b] quinoxalinothiacarbocyanine salt,

1,3-diallyll -ethylimidazo [4,5-b] quinoxalino-3 '-pyrrolo- 2,3-b]quinoxalinocarbocyanine salt,

1'-ethyl-1,3,3-trimethyl-3H-pyrrolo[2,3-b]pyrido-3-pyrrolo [2,3 -b]quinoxalinocarbocyanine salt,

6-chloro-l'-ethyl-1,3-diphenylimidazo [4,5-b] quinoxalino- 3 -pyrrolo[2,3-b] quinoxalinocarbocyanine salt,

l-ethyl-l ,3,3-trimethyl--nitroindo-3 '-pyrrolo [2,3-b]

quinoxalinocarbocyanine salt,

l-butyl-7-chloro-3 '-ethyl-6'-nitro-3-pyrrolo [2,3-b]quinoxalinothiacarbocyanine salt,

1,3-diallyl-1-butyl-7 '-chloroimidazo [4,5 -b] quinoxalino- 3'-pyrrolo[2,3-b] quinoxalinocarbocyanine salt,

1'-butyl-7-chloro-1,3,3-trimethyl-5-nitroindo-3 -pyrrolo- [2,3-bquinoxalinocarbocyanine salt,

3 '-ethyll-methyl-6'-nitro-2-p-tolyl-3 -pyrrolo 2,3-b]

quinoxalinothiacarbocyanine salt,

1,3 -dimethyll'-phenylimidazo [4,5-b] quinolino-3 '-pyr-3'-pyrrolo[2,3-b] quinoxalinocarbocyanine salt,

6-chloro- 1 '-methyl- 1 ,3-diphenyl-2-p-tolylimidazo [4,5 -b]quinoxalino-3 '-pyrrolo [2,3-b] quinoxalinocarbocyanine salt,

1,1,3,3-tetramethyl-5-nitro-2'-p-tolylindo-3 '-pyrrolo- [2,3-b]quinoxalinocarbocyanine salt,

1,1',3,3-tetramethyl-2'-p-tolylpyrrolo[2,3-b]pyrido-3 pyrrolo [2,3-b]quinoxalinocarbocyanine salt,

1 1-dimethyl2, 8-diphenyl-2'-p-tolyl-3 -indolo-3 '-pyrrolo- [2,3-b]quinoxalinocarbocyanine salt,

3'ethyl-6'-nitrol-phenyl-3-pyrrolo [2,3-b] pyrazinothiacarbocyaninesalt,

3-methyl-5-nitro-1'-phenyloXa-3-pyrrolo [2,3-b] pyrazino carbocyaninesalt,

1,3-dimethyll-phenylimidazo[4,5-b]quinolino-3 -pyrrolo [2,3-b]pyrazinocarbocyanine salt,

6-chloro-1,l,3-triphenylimidazo [4,5-b] quinoxalino-3'- pyrrolo 2,3-bpyrazinocarbocyanine salt,

1',3,3-trimethyl-1-phenyl-3-pyrrolo [2,3-b1pyrazino-3H- pyrrolo [2,3-b]pyridocarbocyanine salt, and

1,3 ,3-trimethyl-5-nitro- 1 -phenylindo-3 -pyrrolo 2,3-b]

pyrazinocarbocyanine salt.

18. A direct positive emulsion in accordance with claim 12 in which thesaid silver halide is present in the form of chemically fogged silverhalide grains.

19. A direct positive emulsion in accordance with claim 12 in which thesaid silver halide is present in the form of reduction and gold foggedsilver halide grains.

20. A direct positive emulsion in accordance with claim 12 whichcomprises fogged silver halide grains, said grains being such that atest portion thereof, when coated as a photographic silver halideemulsion on a support to give a maximum density of at least about 1 uponprocessing for 6 minutes at about 68 F. in Kodak DK-SO developer, has amaximum density which is at least about 30% greater than the maximumdensity of an identical coated test portion which is processed for 6minutes at about 68 F. in Kodak DK-SO developer after being bleached forabout 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanine mg 50 Acetic acid (glacial) cc 3.47 Sodium acetate g11.49 'Potassium bromide mg 119 Water to 1 liter.

21. A direct positive emulsion in accordance with claim 12 containing aphotographic color coupler dispersed in coupler solvent.

22. A direct positive photographic emulsion in accord ance with claim 11wherein at least 95%, by weight, of said silver halide grains have asize which is within about 40% of the average grain size.

23. A photographic element comprising a support having thereon at leastone layer containing an emulsion of claim 1.

24. A photographic element comprising a support having thereon at leastone layer containing an emulsion of claim 11.

25. A photographic element comprising a support having thereon at leastone layer containing an emulsion of claim 3.

26. A photographic element comprising a support having thereon at leastone layer containing an emulsion of claim 12.

27. A photographic element comprising a support having thereon at leastone layer containing an emulsion of claim 20.

28. A light-sensitive photographic silver halide emulsion containing atleast one cyanine dye selected from those comprising first and secondnitrogen containing heterocyclic nuclei joined together by a methinelinkage selected from the group consisting of a dimethine linkage and atrimethine linkage; the first of said nuclei being selected from thegroup consisting of a l-alkyl or a l-aryl substitutedpyrrolo[2,3-b]pyrazine nucleus and a l-alkyl or a l-aryl substitutedpyrrolo[2,3-b] quinoxaline nucleus joined at the 3-carbon atom thereofto said linkage; and said second nucleus containing from 5 to 6 atomsand being selected from the group consisting of (a) a heterocyclicnitrogen containing nucleus of the type used in cyanine dyes when saidlinkage is a dimethine linkage; and, (b) when said linkage is atrimethine linkage, said second nucleus is selected from the groupconsisting of a 2-arylindole nucleus, a l-alkyl or a l-aryl substitutedpyrrolo[2,3-b]quinoxaline nucleus and a l-alkyl or a l-aryl substitutedpyrrolo[2,3-b]pyrazine nucleus, each of said nuclei being joined at the3-carbon atom thereof to said trimethine linkage.

29. A light-sensitive emulsion as defined by claim 28 wherein saidcyanine dye is selected from those represented by the following generalformulas:

wherein n represents a positive integer of from 1 to 2; L represents amethine linkage; R represents a member selected from the groupconsisting of an alkyl group, an alkenyl group and an aryl group; Rrepresents a member selected from the group consisting of an alkyl groupand an aryl group; R and R taken individually represents a memberselected from the group consisting of a hydrogen atom, an alkyl group,and an aryl group; R and R taken together represent the non-metallicatoms necessary to complete a pyrrolo[2,3-b]quinoxaline nucleus; Rrepresents a member selected from the group consisting of a hydrogenatom and an aryl group; R represents a member selected from the groupconsisting of an alkyl group, an aryl group and a heterocyclic radicalcontaining from 5 to 6 atoms in the heterocyclic ring and having ahetero nitrogen, oxygen or sulfur atom; X represents an acid anion; Drepresents the non-metallic atoms necessary to complete a nucleusselected from the group consisting of a 2-arylindole nucleus, apyrrolo[2,3-b]pyrazine nucleus and a pyrrolo[2,3-b ]quinoxaline nucleus;and Z represents the non-metallic atoms necessary to complete a nitrogencontaining hererocyclic nucleus of the type used in cyanine dyescontaining from 5 to 6 atoms in the hetero cyclic ring!

